Transfer weights of selected faces to an other bone possible?
I don't know how you named your bones, but each bone should have been assigned to a vertex group named as the bone. See the mesh "object data" properties tab, under "vertex groups". There you can select/deselect, assign/remove vertices from the selected vertex group.

You can control which vertex is in which group, and eventually remove wrong vertices from the wrong leg group and assign them to the right leg group.

Beware that weight painting can add painted vertices to the selected bone's group.

Marco